Most likely it is switched mode, if so watch out as they have extremely high voltages present when powered up IIRC ~20-25KV in the inverter stage, trust me, it hurts!! /ubbthreads/images/graemlins/frown.gif If the PSU has been powered up recently make sure all the capacitors are discharged (make sure anyway) by shorting them out, they can bite too as they store charge.
If it is one of the capacitors then make sure that you put it back in the right way round, this assumes that the cap is an Electrolytic not just a normal polyester, ceramic etc. Reverse polarised electrolytics are really impressive when they go, rather like a firework but they stink the place of fish for days.
For components try either RS Component, Farnell or Maplin may have them however over the last few years they have been carrying less and less components.
You would be as well replacing all the elecrolytic (look like little cans and have a polarity stripe down one side)caps as if 1 has gone the rest usually follow.
You could also try a search for a replacement PSU on EBAY or somewhere like that, i have also found the local tip to be useful at times as most of them have "collectors" for all the elec stuff and they may have a similar model.
The power supply should be very similar across most models of the same era and make.
Cheers,
Jon.